Aircraft typically include firewalls that isolate fire zones from non-fire zones, or one fire zone from another fire zone. In one particular implementation, an aircraft engine includes a firewall that divides the engine into a fire zone and an ignition zone. Typically the fire zone is located in a forward section of the engine and is cooler than the ignition zone, which is located downstream of the fire zone. The firewall is generally annular in shape and located proximate the engine combustor. The firewall surrounds various engine lines, such as fuel and oil lines that provide fuel and oil to the combustor. During operation of the engine, the firewall serves to reduce the possibility of any fuel or oil that has leaked into the fire zone from reaching the ignition zone, where it may ignite and damage the engine and its components. The Federal Aviation Agency (FAA) has stated that firewalls of this type must be capable of containing a fire occurring in the fire zone for a predetermined amount of time. The typical fire test requirements as promulgated by the FAA in Circular 20-135 include withstanding fire at 2,000° F. (1093° C.) for fifteen minutes.
Often, a firewall may include openings that allow system connection equipment, such as ducting, piping and/or wires to extend therethrough to connect the systems to each other. In an aircraft engine, a plurality of pass-through members, such as high pressure (HP) bleed lines, thermal anti-ice (TAI) lines, and electrical wires pass through the firewall and are sealed to prevent or minimize communication of any fuel or oil leakage between the fire zone and the ignition zone. In other cases, sealing (or flow restriction) is needed to minimize leakage across a firewall that separates zones of differential pressure. In some cases, gaps may be present between the pass-through members and the firewall, which, in the unlikely event of a fire, may provide a space through which flames may travel. As a result, specialized firewall seals may need to be included between the equipment and the firewall to prevent the flames from traveling from one side of the firewall to the other.
Attempts have been made to meet the FAA requirement for engine firewalls by sealing the firewall pass-throughs in various ways. Many types of firewall seals have been devised that require the positioning of a portion of a sealing structure through an aperture formed in the firewall. The pass-through line extends through an opening formed in the sealing structure. However, due to typical manufacturing tolerances, these types of structures may be seated in a laterally offset manner from the centerline of the firewall aperture, or may be misaligned, which decreases the sealing effect. In addition, over time damage may occur to the portion of the sealing structure that is in contact with the ignition zone.
Additional attempts at sealing firewall pass-throughs include the use of a fireproof, reinforced silicone primary seal or boot that provides a barrier between the fire zone and the ignition zone by surrounding structural tubing that extends through the firewall. Testing for fireproofness of this type of single component structure often results in failure with ignition on the backside of the primary seal. Still other types of fittings include the use of bulkhead connectors, close tolerance fittings, single purpose penetration ducting or flanged connections at the firewall.
Although the above-mentioned firewall seals are in many instances adequate for preventing flames from traveling through the firewall, they suffer from certain drawbacks. In particular, many of the fittings do not provide adequate means to eliminate backside ignition, may include a number of components that together are relatively heavy and may undesirable increase aircraft weight, and/or may be relatively costly to implement. In addition, many of the fittings rigidly attach the system connection equipment to the firewall, which may unnecessarily increase the load on the fitting and/or the firewall.
It should thus be appreciated from the above that it would be desirable to provide a firewall pass-through seal assembly that complies with the FAA fireproof standard and eliminates damage to engine components due to seal failure. Furthermore, there is a need for a seal assembly that is relatively lightweight and inexpensive to implement. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.